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RISC-V: use PC-relative addressing instead of absolute addressing #550

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Merged
xavierleroy merged 1 commit into from
May 29, 2025
Merged

RISC-V: use PC-relative addressing instead of absolute addressing #550

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20 changes: 12 additions & 8 deletions riscV/TargetPrinter.ml
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Original file line number Diff line number Diff line change
Expand Up @@ -115,10 +115,7 @@ module Target : TARGET =
assert (ofs = Integers.Ptrofs.zero);
fprintf oc " la %a, %s\n" ireg r (extern_atom id)
end else begin
fprintf oc " lui %a, %%hi(%a)\n"
ireg r symbol_offset (id, ofs);
fprintf oc " addi %a, %a, %%lo(%a)\n"
ireg r ireg r symbol_offset (id, ofs)
fprintf oc " lla %a, %a\n" ireg r symbol_offset (id, ofs)
end

(* Emit .file / .loc debugging directives *)
Expand All @@ -138,9 +135,14 @@ module Target : TARGET =

(* Offset part of a load or store *)

let latest_auipc : (ident * Integers.Ptrofs.int) option ref = ref None

let offset oc = function
| Ofsimm n -> ptrofs oc n
| Ofslow(id, ofs) -> fprintf oc "%%lo(%a)" symbol_offset (id, ofs)
| Ofsimm n ->
ptrofs oc n
| Ofslow(id, ofs) ->
assert (!latest_auipc = Some(id, ofs));
fprintf oc "%%pcrel_lo(1b)"

(* Printing of instructions *)
let print_instruction oc = function
Expand Down Expand Up @@ -495,7 +497,8 @@ module Target : TARGET =
| Ploadsymbol(rd, id, ofs) ->
loadsymbol oc rd id ofs
| Ploadsymbol_high(rd, id, ofs) ->
fprintf oc " lui %a, %%hi(%a)\n" ireg rd symbol_offset (id, ofs)
fprintf oc "1: auipc %a, %%pcrel_hi(%a)\n" ireg rd symbol_offset (id, ofs);
latest_auipc := Some(id, ofs)
| Ploadli(rd, n) ->
let d = camlint64_of_coqint n in
let lbl = label_literal64 d in
Expand All @@ -516,7 +519,7 @@ module Target : TARGET =
List.iter (fun l -> fprintf oc "%a " print_label l) tbl;
fprintf oc "]\n";
fprintf oc " sll x5, %a, 2\n" ireg r;
fprintf oc " la x31, %a\n" label lbl;
fprintf oc " lla x31, %a\n" label lbl;
fprintf oc " add x5, x31, x5\n";
fprintf oc " lw x5, 0(x5)\n";
fprintf oc " add x5, x31, x5\n";
Expand Down Expand Up @@ -584,6 +587,7 @@ module Target : TARGET =

let print_instructions oc fn =
current_function_sig := fn.fn_sig;
latest_auipc := None;
List.iter (print_instruction oc) fn.fn_code


Expand Down